{"id":"DEBIAN-CVE-2026-62949","details":"AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Prior to 2.24.0, _process_channel_open and _process_channel_open_confirmation in asyncssh/connection.py accept a peer-supplied send_pktsize value of zero. When channel data reaches SSHChannel._flush_send_buf in asyncssh/channel.py, the zero value causes each loop iteration to slice and remove zero bytes without reducing the send window, leaving the synchronous loop permanently true with no await point. A malicious SSH server can trigger the client path through SSH_MSG_CHANNEL_OPEN_CONFIRMATION before the first channel write, while an authenticated client can trigger the server path through SSH_MSG_CHANNEL_OPEN and freeze every current and future connection handled by the process. This vulnerability is fixed in 2.24.0.","modified":"2026-09-18T17:00:08.489470646Z","published":"2026-09-16T20:17:26.220Z","upstream":["CVE-2026-62949"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-62949"}],"affected":[{"package":{"name":"python-asyncssh","ecosystem":"Debian:12","purl":"pkg:deb/debian/python-asyncssh?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.10.1-2","2.10.1-2+deb12u1","2.10.1-2+deb12u2","2.15.0-1","2.16.0-1","2.17.0-1","2.17.0-2","2.18.0-1","2.19.0-1","2.20.0-1","2.21.0-1","2.21.1-1","2.22.0-1","2.22.0-2","2.23.0-1","2.24.0-1","2.24.0-2"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Debian:13","purl":"pkg:deb/debian/python-asyncssh?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.20.0-1","2.21.0-1","2.21.1-1","2.22.0-1","2.22.0-2","2.23.0-1","2.24.0-1","2.24.0-2"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-62949.json"}},{"package":{"name":"python-asyncssh","ecosystem":"Debian:14","purl":"pkg:deb/debian/python-asyncssh?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.20.0-1","2.21.0-1","2.21.1-1","2.22.0-1","2.22.0-2","2.23.0-1","2.24.0-1","2.24.0-2"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-62949.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}